This invention relates generally to dental implants, and, more particularly, to submergible screw-type implants.
Screw-type implants are well known in the art. U.S. Pat. No. 3,499,222 of L. I. Linkow et al. (the xe2x80x9c""222 patentxe2x80x9d) discloses screw-type implants that may be buried in the alveolar ridge crest bone of a patient in an edentulous region. The implant has a threaded lower portion that may be screwed into an opening created in the bone after the tissue has been displaced. A coronal portion protrudes above the bone and is used to support an artificial dental appliance, e.g., an artificial tooth or bridge.
More recently, submergible implants have been created in which the threaded portions of the implants can be completely embedded in the bone. They may then be covered with tissue and allowed to remain in place while new bone grows around the implant and through vent holes in it. Once it is firmly anchored in new bone, the tissue is reopened and an upper post portion is screwed into the implant portion and is used to mount the artificial dental device. An example of this type of implant can be found in U.S. Pat. No. 4,713,004 of L. I. Linkow et al. (the xe2x80x9c""004 patentxe2x80x9d).
A prior surgical method for installing an implant portion involved creating an incision in the tissue covering the alveolar ridge crest bone. This underlying bone was then exposed and a cylindrical bore was drilled into the bone at a depth sufficient to hold the implant portion of the device. The bore was made slightly smaller in diameter than the implant device and was at an angle that would allow it to engage the major portion of the available bone. Then a bore tap is used to create threads in the bore, after which the implant device was threaded into the remaining bone.
Alternatively, an implant may be embedded and not covered with tissue. This eliminates the need to reopen the tissue later to mount an artificial dental device.
It is also well known in the art, e.g., from the ""004 patent, that a channel through threads on the implant will create a cutting edge so the implant becomes self-tapping (e.g., end cutting). When installing an implant portion in the patient""s bone, it is advantageous if the implant is self-tapping because it causes the implant to be anchored more securely. If such a self-tapping implant is used, a bone tap is not needed and the implant is threaded directly into the bone utilizing the self-tapping threads created by the channel along the length of its threads.
Also, it is advantageous if the bone chips created during a self-tapping operation are deposited into the bore or opening, because these autogenous chips promote faster bone regenerative growth. The channel guides these bone chips, which are created during the self threading of the implant, toward the base of the bore in the bone. In particular, during the insertion procedure with a self-tapping implant, bone chips are removed from the walls of the bore while forming the grooves in the bone that match the threads in the implant. These bone chips drop along the channel to the base of the bore and help to promote the growth of new bone that firmly anchors the implant in place.
When a tooth is extracted, it leaves behind a rather large conically-shaped cavity, which does not lend itself to the insertion of a cylindrical implant if an artificial tooth is to be substituted for the removed tooth. One technique for overcoming this problem of the extracted tooth is to expose the cavity in the bone, fill the extraction site with bone graft material, such as autogenous, allographic or xerographic material, and then cover the site with gum tissue for a period of time sufficient for new bone to grow into and fill the cavity, e.g., with a mixture of the grafted bone and newly grown bone. Then a cylindrical bore is drilled at the site and a dental implant is installed in the usual manner. However, this requires that the patient live with an edentulous area without a functional prosthesis for a long period of time.
As an alternative, the implant can have a shape that is not cylindrical, but instead is conical or U-shaped, in order that it more nearly fits the dimensions of an extraction site. Such implants may be found in U.S. Pat. No. 4,521,192 of L. I. Linkow (the xe2x80x9c""192 patentxe2x80x9d), and U.S. Pat. No. 2,609,604 of B. F. Sprague (the xe2x80x9c""604 patentxe2x80x9d). As the slope of the conical shape of the extraction site cannot be predicted in advance, these implants cannot be made self tapping. As a result, no pressure can be applied to these implants for a significant period of time, i.e., until existing bone has grown around the implant to anchor it in place. In addition, as a self-tapping implant is not used, there may not be intimate contact between the implant and the new bone, so the implant may eventually fail, even if a significant amount of time is allowed to pass before an artificial tooth is mounted on the implant and it is put into use.
It would be of great benefit when replacing extracted teeth with dental implants to use an implant that compensates for the shape of the extraction socket, is at least partially self-tapping for initial implant stability and assures relatively intimate contact between the implant and new bone so that the implant can be put into service relatively soon after the procedure and still have a low probability of subsequent failure.
The present invention is directed to a dental implant that may be used at the site of a recent tooth extraction and can be put into service in a reasonably short period of time. This implant has a lower self-tapping portion and an upper portion covered with a sintered material that is osteopromotive and osteoretentive so to promote adhesion between the implant and the surrounding bone.
In a preferred form of an illustrative embodiment, the implant is of the submergible screw type with an upper portion having a conical shape and a lower cylindrical portion having threads. A longitudinal channel or slot extends through the threads on the lower cylindrical portion so as to make the threads self-tapping. The channel is wider toward its apical end.
One side of the channel is at a right angle or acute angle to the implant circumference so as to create a cutting edge that forms the self-tapping capability for the implant. The other side of the channel can be at an oblique angle to the circumference.
At least a portion of the exterior surface of the upper conical portion of the implant is sintered with a plurality of spherical projections made of a material suitable for bone integration, the spaces in between forming a porous surface.
At the lower or apical portion of the implant there is a vent or opening to allow for autogenous bone chips created during self-tapping to enter therein when the implant is screwed into the bone socket.